It is a colorless, odorless, tasteless, extremely poisonous gas that is less dense than air under ordinary conditions. It burns in air with a characteristic blue flame, producing carbon dioxide. It is a component of the artificial fuels producer gas and water gas.

As a reducing agent, it removes oxygen from many compounds and is used in the reduction of metals from the ores. When air containing as little as 0.1% carbon monoxide by volume is inhaled, the oxygen of haemoglobin is replaced by the carbon monoxide, resulting in fatal oxygen starvation throughout the body.